This invention relates generally to a high pressure tank system, and more particularly to a high pressure tank system with a pressure retention valve with an integrated valve.
The tank vessel is a key component in a high pressure storage system. High pressure storage systems are used in a wide variety of applications including vehicle applications, such as vehicles run by hydrogen, or compressed natural gas (CNG). It is desirable to use fiber composite vessels (known as “type 4” vessels) for the tank because they have a good storage to weight ratio. Type 4 vessels have two layers: an outer layer, made of a carbon fiber matrix for example, designed to bear the mechanical load; and an inner layer, or liner, made of a bubble of plastic or aluminum, designed to prevent leaking.
To ensure that the liner is firmly supported by the outer layer, a minimum pressure should be maintained in the tank at all times. If pressurizing is started from an initial pressure below the minimum pressure, the liner might rupture, and the contents would flow through the outer layer into the environment.
Conventional gas tank systems use an electrical pressure sensor signal to maintain the minimum pressure. The signal is evaluated in a vehicle controller. If the minimum pressure is reached, the tank valve(s) are closed. This system is an active system, requiring a controller, pressure sensor, algorithm, and electrical power to control the minimum pressure. The residual non-usable gas amount depends on the accuracy of the pressure sensor. However, the pressure sensors have a tolerance limitation which has to be considered, and they do not have good accuracy at low pressure. In addition, drift of the sensor signal can occur over time. Due to the high deviation in the low pressure range, a significant pressure safety margin has to be added to the nominal minimum operation pressure. This leads to a reduction in the amount of usable hydrogen/gas mass, and thus to a lower range for the vehicle.